The invention relates to a signal analysing circuit for a periodically occurring signal. The signal analysis is effected separately in a first number of distinct portions of at least a portion of each signal period contained in a second number of consecutive signal periods. The circuit incorporates a signal source having an output for supplying the periodically occurring signal, a store having separate store locations for storing in each of them information corresponding to signal voltages which always occur in one of the distinct portions of each signal portion contained in the second number of consecutive signal periods. A time signal generator is provided for synchronously controlling the signal source to supply the periodically occurring signals. The store having the separate store locations is present in a third number which is a multiple of said first number.
Such a signal analysing circuit is disclosed in the U.S. Pat. No. 3,743,772, which has for its object the analysis of a video signal as a periodically occurring signal having a signal scanning period and a signal blanking period. In the patent the signal analysis is effected in a line scanning period for ultimately obtaining correction of shading distortion. Such distortion occurs when a television pick-up which operates as a signal source is uniformly illuminated and the resulting video signal results on display in a non-uniformly luminescing picture. The signal analysis is effected in regions of the picture which are defined by rows and columns. The number of columns of regions correspond to the first number and the number of regions per column depends on the number of television lines from which the picture is assembled and the second number of lines per region. With each region occurring in the third number there corresponds a separate store location in the store, in which store location a correction value for the local distortion is to be stored.
The patent briefly describes how the store can be filled with information. For that purpose the signal produced by the signal sources is compared with a reference value and the difference is stored as a correction value in the associated store location through a controlled gate. For the synchronous control of the signal source, the gate, and the store, the time signal generator acts as a correlator.
The patent does not describe in greater detail how filling the separate store locations is effected.